Exothermic

In thermodynamics, the word exothermic "outside heating" describes a process or reaction that releases energy usually in the form of heat, but it can also release energy in form of light (e.g. explosions), sound, or electricity (e.g. a battery). Its etymology stems from the Greek prefix "exo-," meaning “outside” and the Greek word "thermein", meaning “to heat”. The term “exothermic” was first coined by Marcellin Berthelot. The opposite of an exothermic process is an endothermic process, one that absorbs energy in the form of heat.

The concept is frequently applied in physical sciences to chemical reactions, where chemical bond energy is converted to thermal energy (heat).

Overview

Exothermic refers to a transformation in which a system releases energy (heat) to the surroundings:

:Q < 0

When the transformation occurs at constant pressure:

:"∆H < 0"

and constant volume:

:"∆U < 0"

In an adiabatic system (e.g. a system that does not give off heat to the surroundings), an exothermic process results in an increase in temperature. [cite book | last = Perrot | first = Pierre | title = A to Z of Thermodynamics | publisher = Oxford University Press | year = 1998 | id = ISBN 0-19-856552-6 ]

In chemical reactions, the heat that is released is in the form of electromagnetic energy. The loss of kinetic energy via reacting electrons causes light to be released. This light is equivalent in energy to the stabilization energy of the energy for the chemical reaction, i.e. the bond energy. This light that is released can be absorbed by other molecules in solution to give rise to molecular vibrations or rotations, which gives rise to the classical understanding of heat. In contrast, when endothermic reactions occur, energy is absorbed to place an electron in a higher energy state, such that the electron can associate with another atom to form another chemical complex. The loss of energy within solution is absorbed by the endothermic reaction and therefore is a loss of heat. This is the physical understanding of exothermic and endothermic reactions within solution.

Examples

Some examples of exothermic processes are: [ [http://antoine.frostburg.edu/chem/senese/101/thermo/faq/exothermic-endothermic-examples.shtml Exothermic - Endothermic examples] ]
* Condensation of rain from water vapour
* Combustion of fuels such as wood, coal and oil
* Mixing water and strong acids
* Mixing alkalis and acids
* The setting of cement and concrete
* Most polymerisation reactions such as the setting of epoxy resin
* Thermite reaction

Implications for chemical reactions

Chemical exothermic reactions are generally more spontaneous than their counterparts, endothermic reactions. In a thermochemical reaction that is exothermic, the heat may be listed among the products of the reaction.

ee also

* Calorimetry
* Chemical thermodynamics
* Differential scanning calorimetry
* Endergonic
* Endergonic reaction
* Exergonic
* Exergonic reaction

External links

* http://chemistry.about.com/b/a/184556.htm Observe exothermic reactions in a simple experiment

References


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Look at other dictionaries:

  • Exothermic — Ex o*ther mic, a. [Pref. exo + thermic.] (Chem.) Characterized by, or formed with, evolution of heat; as, an exothermic reaction; opposed to {endothermic}. [Webster 1913 Suppl.] …   The Collaborative International Dictionary of English

  • Exothermic — Exothermic. См. Экзотермический. (Источник: «Металлы и сплавы. Справочник.» Под редакцией Ю.П. Солнцева; НПО Профессионал , НПО Мир и семья ; Санкт Петербург, 2003 г.) …   Словарь металлургических терминов

  • exothermic — 1879, from Fr. exothermique (1879), from EXO (Cf. exo ) + thermique, ultimately from Gk. therme heat (see THERMAL (Cf. thermal)) …   Etymology dictionary

  • exothermic — ► ADJECTIVE Chemistry ▪ (of a reaction) accompanied by the release of heat. The opposite of ENDOTHERMIC(Cf. ↑endothermic) …   English terms dictionary

  • exothermic — [ek΄sō thʉr′mik, ek΄səthʉr′mik] adj. [ EXO + THERMIC] designating or of a chemical change in which there is a liberation of heat, as in combustion: also exothermal …   English World dictionary

  • exothermic — Reactions that proceed with release of enthalpy (heat energy) are termed exothermic. See: endothermic …   Petroleum refining glossary

  • exothermic —    A material which gives off heat as it cures is described as exothermic. Also see temperature …   Glossary of Art Terms

  • exothermic — UK [ˈeksəʊˌθɜː(r)mɪk] / US [ˈeksoʊˌθɜrmɪk] adjective chemistry an exothermic reaction is a chemical reaction in which heat is produced, not absorbed See: endothermic …   English dictionary

  • exothermic — egzoterminis procesas statusas T sritis ekologija ir aplinkotyra apibrėžtis Vyksmas,kai išsiskiria šiluma, pvz., cheminė reakcija, per kurią į aplinką išsiskiria šiluma. atitikmenys: angl. exothermic vok. exothermisch rus. экзотермический процесс …   Ekologijos terminų aiškinamasis žodynas

  • exothermic — adjective Etymology: International Scientific Vocabulary Date: 1884 characterized by or formed with evolution of heat • exothermically adverb • exothermicity noun …   New Collegiate Dictionary

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